1. Field of the Invention
The present invention generally relates to a liquid crystal display panel, and more particularly to a method and structure that permits photon sealing of substrates, such as flat panel liquid crystal display (LCD) substrates, in a manner that prevents shadowing.
2. Description of the Related Art
Previously, conventional methods fabricated liquid crystal panels by attaching two panel substrates (e.g., with one panel containing the circuitry, and the other panel containing the color filter) and bonding them together with a thermally-curable glue seal. The glue seal is applied near the periphery of the panel, leaving on the order of a few millimeters of the panel""s periphery without a glue seal.
Bonding generally occurs by baking the assembly and thermally curing the polymeric glue seal, typically at temperatures on the order of 180-200xc2x0 C. for periods on the order of 1-3 hours.
After baking, the assembled panel is placed in a vacuum chamber where the end containing the open portion is dipped into the liquid crystal. The vacuum chamber is then back filled with gas (e.g., nitrogen) to force the liquid crystal into the narrow space (e.g., typically on the order of about 5 microns) between the two substrates.
After filling, the opening is closed off by a second sealant that polymerizes with UV radiation, thereby forming the final seal.
Recently, U.S. Pat. No. 5,263,888, incorporated herein by reference, disclosed a process which no longer utilizes a nearly fully sealed panel prior to filling with a liquid crystal.
Instead, one substrate placed in a horizontal position receives droplets of liquid crystal and a fillet of peripheral glue seal. The second substrate is placed over the first, aligned with respect to the first substrate and then is subjected to ultraviolet (UV) radiation which cures the glue seal. This process has the potential for saving many hours of process time since the baking and vacuum fill procedure associated with the conventional method previously described take many hours.
However, a problem with the above-described method of U.S. Pat. No. 5,263,888 is that metal signal and gate lines that lead from the interior of the panel circuitry to the exterior are xe2x80x9cshadowedxe2x80x9d upon exposure to the UV radiation used for curing. That is, shadowing normally occurs when the electrical lines in the region of the glue seal are opaque to the radiation used for curing the glue seal, preventing the optical radiation from curing the glue seal in the region directly below and in contact with that portion of the electrically conducting lines.
Thus, when the glue seal is photolytically activated to cause it to set or polymerize, any region shadowed by a thin film or other circuitry on the inside of the upper panel will cause some shadowing on the surface below when the radiation is incident on the upper panel. The shadowing can result in the glue immediately in contact with the thin film circuitry to remain uncured. This may well result in a deleterious effect of having the glue come in contact with, for example, a liquid crystal material, thereby leading to a xe2x80x9cpoisoningxe2x80x9d (contamination) of the liquid crystal.
It is generally not possible to UV expose from the second substrate to avoid the shadowing since that substrate contains a peripheral border that is essentially totally opaque.
Further, while other suggestions have been put forth to cure this shadowed region (e.g., see the above-mentioned copending U.S. patent applications Ser. No. 09/425,701 and 09/425,711 to Robert J. von Gutfeld et al., incorporated herein by reference), no simple method has been suggested to avoid the shadowing problem.
In view of the foregoing and other problems of the conventional methods and structures, an object of the present invention is to provide a method and structure in which the above-described shadowing problem is overcome.
In a first aspect of the present invention, a structure (and method of forming the structure) includes an electrically conducting pattern on at least one of two substrates to be combined with the other of the two substrates via a seal. The conducting pattern in the region of the seal for attaching the two substrates is at least transmissive to a radiation for curing the seal under the pattern to affix the two substrates.
In a second aspect, a liquid crystal display (LCD) panel includes first and second substrates coupled together by a seal, a liquid crystal material formed between the first and second substrates, and an electrically conducting pattern formed on at least one of the first and second substrates such that the conducting pattern in a region of the seal comprises a material at least transmissive to radiation for curing the seal under the pattern, in at least the region of the seal, to couple the two substrates together.
With the unique and unobvious features of the present invention, a method and structure are provided that utilize transmissive electrical lines that are at least partially transmitting to the UV radiation required for photolytically curing the glue seal. Preferably, these lines are very short (e.g., on the order of about 0.5 to about 3 mm) and only extend in the region of the glue seal.
Further, no additional photolithographic step is required for this pattern so that cost is kept at a minimum.
Preferably, any one of a number of materials can be used for the signal and gate lines in the peripheral region of the glue seal so long as such materials permit sufficient UV radiation to penetrate through these lines to seal the glue that lies immediately beneath these lines.
Thus, with the invention, shadowing is eliminated and the glue seal will be cured at all locations where UV radiation is incident in the peripheral region to form a good permanent seal.